Continuous casting equipment produces a slab from refined molten steel received from steel-making equipment. In general, continuous casting equipment includes: a ladle in which molten steel subject to refining in steel-making equipment is received; a tundish disposed under the ladle to receive the molten steel from the ladle, and temporarily storing the molten steel; a mold disposed under the tundish to receive the molten steel from the tundish and solidifying the molten steel in a slab-like shape; and a segment disposed under the mold and performing a series of forming operations to manufacture a slab. The tundish receives molten steel from the ladle and provides the mold with the molten steel. The tundish functions to separate an inclusion by floating, to stabilize slag, to prevent molten steel from being re-oxidized, and to distribute the molten steel to a strand. The tundish is manufactured in a hollow container shape and has a space for receiving molten steel therein. A molten steel tap hole is formed in the bottom surface of the tundish, an upper nozzle is insertedly attached to the molten steel tap hole, and the upper nozzle is connected to a submerged entry nozzle provided under the tundish. A predetermined amount of molten steel is received in the tundish, and the molten steel is introduced into the submerged entry nozzle through the molten steel tap hole and the upper nozzle connected to the molten steel tap hole. The molten steel introduced into the submerged entry nozzle is provided to the mold and is solidified in a slab-like shape.
Various kinds of inclusions, such as alumina inclusions may be mixed into the molten steel in the tundish. Various kinds of inclusions mixed into the molten steel are separated by floatation and removed, but a portion thereof is not removed and remains in the molten steel. The remaining inclusion adheres to the submerged entry nozzle to form a skull while the molten steel passes through the submerged entry nozzle to be provided to the mold. The inclusion adhering to the submerged entry nozzle irregularly reduces the inner diameter of the submerged entry nozzle, and thus changes the tap amount of molten steel during an operation. Therefore, molten steel flow in the mold becomes unstable, for example, a deflected flow of molten steel is generated in the mold, a vertical change of the molten steel surface in the mold is caused, or the like. When the molten steel flow inside the mold is unstable, a defect may be easily generated in a solidified shell, and thus, not only the quality of a slab is deteriorated but also a breakout of the slab is generated during an operation, thereby causing a case of operation stoppage. Also, when a great amount of inclusion adheres to the submerged nozzle, a case of nozzle clogging may occur and thus may cause operation stoppage. Hereinafter, as described above, the irregular reduction in the inner diameter of the submerged entry nozzle due to the skull formed by inclusion adhering to the submerged entry nozzle and the clogging of the submerged entry nozzle will be referred to as nozzle clogging, for convenience in description. To suppress the above-mentioned nozzle clogging, for example, Japanese Patent Application Laid-Open Publication No. 2011-147940, Japanese Patent Application Laid-Open Publication No. 2012-210647, Japanese Patent Application Laid-Open Publication No. 2005-199339, and Japanese Patent Application Laid-Open Publication No. 2005-066689 disclose a continuous casting method which derives an electrochemical deoxidization reaction of an inclusion adhering to the submerged entry nozzle by providing an electrode in the submerged entry nozzle. Here, the deoxidization reaction rate is changed according to the intensity of current applied to the electrode, and when the intensity of the applied current is changed corresponding to a current adhesion state, the nozzle clogging can be suppressed more effectively. However, the above-mentioned patent documents disclose a continuous casting method which only suppresses adhesion of a skull by applying a predetermined intensity of current to the inner wall of the submerged entry nozzle, but do not disclose a method capable of responding to the adhesion state of the skull by quickly measuring the adhesion state of an inclusion to an inside the nozzle. Accordingly, to effectively remove the adhering skull corresponding to the adhering state of the skull, a continuous casting method capable of quickly measuring the inclusion adhering state is required.
Meanwhile, in related arts, there is a method for determining whether the nozzle clogging occurs, wherein the change of molten steel surface in the mold is measured to determine whether the nozzle clogging occurs. However, this method indirectly measures the adhesion state of inclusion to the nozzle through the change in molten steel flow, the change being a phenomenon occurring because an inclusion adheres to the nozzle, and it is impossible to quickly detect the states of generation and adhesion of inclusions on the inner wall of the nozzle through this method. Thus, a method for quickly measuring the inclusion adhesion state inside the nozzle to suppress or prevent the nozzle clogging which may be generated during an operation.
(Prior Art Document) Japanese Patent Application Laid-Open Publication No. 2011-147940
(Prior Art Document) Japanese Patent Application Laid-Open Publication No. 2012-210647
(Prior Art Document) Japanese Patent Application Laid-Open Publication No. 2005-199339
(Prior Art Document) Japanese Patent Application Laid-Open Publication No. 2005-066689